Download Newton`s Laws

Newton's Laws
Newton's Law of Inertia
• According to Newton's first law, an object in
motion continues in motion with the same
speed and in the same direction unless acted
upon by an unbalanced force. It is the natural
tendency of objects to keep on doing what
they're doing. All objects resist changes in
their state of motion. In the absence of an
unbalanced force, an object in motion will
maintain its state of motion. This is often
called the law of inertia.
Now perhaps you will be convince of the
need to wear your seat belt.
Remember it's the law - the law of inertia.
If the car were to abruptly stop and the seat belts were not
being worn, then the passengers in motion would
continue in motion. Assuming a negligible amount of
friction between the passengers and the seats, the
passengers would likely be propelled from the car and be
hurled into the air. Once they leave the car, the passengers
becomes projectiles and continue in projectile-like motion.
• If the motorcycle were to abruptly stop, then
the rider in motion would continue in motion.
The rider would likely be propelled from the
motorcycle and be hurled into the air. Once
they leave the motorcycle, the rider becomes
a projectile and continues in projectile-like
motion.
But why then are motorcycles not
equipped with safety harnesses?
If the truck were to abruptly stop and the straps were
no longer functioning, then the ladder in motion
would continue in motion. Assuming a negligible
amount of friction between the truck and the
ladder, the ladder would slide off the top of the
truck and be hurled into the air. Once it leaves the
roof of the truck, it becomes a projectile and
continues in projectile-like motion.
Elephant and Feather - Free Fall
• Suppose that an elephant and a
feather are dropped off a very tall
building from the same height at
the same time. Suppose also that
air resistance could somehow be
eliminated such that neither the
elephant nor the feather would
experience any air drag during the
course of their fall. Which object the elephant or the feather - will hit
the ground first?
TRUE or FALSE:
• The elephant and the feather each have the same force of gravity.
• The elephant has more mass, yet both elephant and feather
experience the same force of gravity.
• The elephant experiences a greater force of gravity, yet both the
elephant and the feather have the same mass.
• On earth, all objects (whether an elephant or a feather) have the
same force of gravity.
• The elephant weighs more than the feather, yet they each have
the same mass.
• The elephant clearly has more mass than the feather, yet they
each weigh the same.
• The elephant clearly has more mass than the feather, yet the
amount of gravity (force) is the same for each.
• The elephant has the greatest acceleration, yet the amount of
gravity is the same for each.
• A simple rule to bear in mind is that all objects
(regardless of their mass) experience the same
acceleration when in a state of free fall. When
the only force is gravity, the acceleration is the
same value for all objects. On Earth, this
acceleration value is 9.8 m/s2. This is such an
important value in physics that it is given a
special name - the acceleration of gravity - and
a special symbol - g.
• But what about air resistance? Isn't it
nonrealistic to ignore the influence of air
resistance upon the two object? In the
presence of air resistance, the elephant is sure
to fall faster. Right?
why does the elephant fall faster?
TRUE or FALSE:
The elephant encounters a smaller force of air resistance than
the feather and therefore falls faster.
The elephant has a greater acceleration of gravity than the
feather and therefore falls faster.
Both elephant and feather have the same force of gravity, yet
the acceleration of gravity is greatest for the elephant.
Both elephant and feather have the same force of gravity, yet
the feather experiences a greater air resistance.
Each object experiences the same amount of air resistance,
yet the elephant experiences the greatest force of gravity
TRUE or FALSE:
• Each object experiences the same amount of air resistance,
yet the feather experiences the greatest force of gravity.
• The feather weighs more than the elephant, and therefore
will not accelerate as rapidly as the elephant.
• Both elephant and feather weigh the same amount, yet the
greater mass of the feather leads to a smaller acceleration.
• The elephant experiences less air resistance and than the
feather and thus reaches a larger terminal velocity.
• The feather experiences more air resistance than the
elephant and thus reaches a smaller terminal velocity.
• The elephant and the feather encounter the same amount
of air resistance, yet the elephant has a greater terminal
velocity.
All false
• The elephant and the feather are each being pulled downward due
to the force of gravity.
• When initially dropped, this force of gravity is an unbalanced force.
Thus, both elephant and feather begin to accelerate
• As the elephant and the feather begin to gain speed, they
encounter the upward force of air resistance.
• Air resistance is the result of an object plowing through a layer of
air and colliding with air molecules. The more air molecules which
an object collides with, the greater the air resistance force.
Subsequently, the amount of air resistance is dependent upon the
speed of the falling object and the surface area of the falling object.
Based on surface area alone, it is safe to assume that (for the same
speed) the elephant would encounter more air resistance than the
feather.
• But why then does the elephant, which
encounters more air resistance than the
feather, fall faster?
• After all doesn't air resistance act to slow an
object down
• So in conclusion, the elephant falls faster than
the feather because it never reaches a
terminal velocity; it continues to accelerate as
it falls (accumulating more and more air
resistance), approaching a terminal velocity
yet never reaching it.
• On the other hand, the feather quickly
reaches a terminal velocity. Not requiring
much air resistance before it ceases its
acceleration, the feather obtains the state of
terminal velocity in an early stage of its fall.
The small terminal velocity of the feather
means that the remainder of its fall will occur
with a small terminal velocity.
Skydiving
• As the skydiver falls, he encounters the force of
air resistance. The amount of air resistance is
dependent upon two variables:
• The speed of the skydiver
• The cross-sectional area of the skydiver
The amount of air resistance is
dependent upon two variables:
• The speed of the skydiver
• The cross-sectional area of the skydiver